A longitudinal adjuster of this type is disclosed in DE 100 50 959 B4, in which the first seat track has two opposing rows of detents and three detent plates are mounted in the second seat track. Each detent plate has on both longitudinal sides of the base body three teeth which protrude through slots of the second seat track and which may engage in the detents. In the normal case, locking without clearance is implemented by means of at least one of the detent plates. In the event of a crash, webs between the slots are deformed so that at least one further detent plate is effective above a specific load.